The stabilization of the position of a rotational mass in inertial space on a moving platform (e.g., a rotary weapon unit mounted on a vehicle) is usually not achieved by controlling the rotational speed of the mass relative to the platform, but by controlling the rotational speed or the position of the rotational mass in inertial space by means of a gyroscope. The output signal of the gyroscope is supplied to a control circuit that compares the deviation of the actual position of the mass in space with a commanded position, and produces an error signal that is supplied to the stabilization drive.
The accuracy of the stabilized inertial position (i.e., the position of the mass in a coordinate unit moving linearly at constant speed) is influenced by various factors, such as the friction of the drive, the manner by which the rotational mass is held, the magnitude of the mass unbalance, and the rotary moment of inertia of the rotating mass. In a moving platform with a stabilized rotational mass, the rotating driving masses have to be accelerated or decelerated in a manner coordinated with movement of the platform during the same interval of time. Each error between these two coordinated motions results in a corresponding error in the stabilization angle. Depending on the extent of deviation from the desired stabilization angle, high or low stabilization quality is achieved with such a stabilization drive. In order to achieve high stabilization quality, various methods for stabilizing the position of a rotational mass are known and will be briefly described below.
The adjustment drive can be designed such that the inertia of the driving masses is very small. This can permit the use of direct drives (e.g., annular torque motors) which are constructed about the rotational axis of a drive without any gears. Such direct drives have to supply all of the torque necessary for to adjust the position of the rotational mass, and to eliminate, or at least keep small, the influence of disturbances attributable to the rotating drive parts' own inertia. Such direct drives are known for stabilizing optical devices. For the stabilization of weapon units, corresponding direct drives have been developed theoretically, but not in practice. For weapon units, only adjustment drives with a small gear ratio and a correspondingly-reduced drive mass have been employed. These adjustment drives are only suitable for rotational masses with a small out-of-balance moments, as the holding torque exerted by the drive motor to counter an out-of-balance moment becomes larger as the mass and/or gear ratio becomes larger.
More recent developments in armored vehicles have lead to an increase of the out-of-balance moment of the weapon unit, which is largely attributable to longer barrels of the weapon unit. Due to the increase of the unbalance moment, the requirements on the stabilization drive have been increased, as the stabilization behaviour of such weapons with respect to well-balanced rotational masses is clearly influenced by the vehicle movement in the vertical direction, as well as in the horizontal or azimuthal direction. Due to the increase in the unbalance of the mass, the sensitivity to disturbances in the vertical direction has also increased, with a resulting negative influence on stabilization quality.
Another attempt to reduce the influence of the inertia of the drive masses involves the use of an auxiliary gyroscope for measuring the rotational movement of the moving platform about the rotational axis of the movable mass. According to this method, the measuring signal of this auxiliary gyroscope is supplied to an internal control circuit and is used to cause an anticipatory rotation of the driven masses before the actual measuring gyroscope records an error. However, the practicality of using an auxiliary gyroscope is limited, as the reaction time between generation of the anticipatory signal from the auxiliary gyroscope and the response of the driven rotational mass is too short.
An improvement of stabilization quality can also be achieved if the force exerted by the adjustment drive on the rotational mass, and also the reaction force exerted by the drive on the platform, is measured and used in an internal stabilization control circuit for controlling the adjustment drive. This method is known in hydraulic drives where the differential pressure between the two opposed chambers in a drive cylinder is measured. In this case, the differential pressure is proportional to the force the drive exerts on the rotational mass, and, reactively, on the platform. The force acting in such a hydraulic drive system is proportional to the acceleration of the rotational mass relative to the platform (i.e., is proportional to the derivative of the velocity of the mass relative to the platform with respect to time). With harmonic excitation, this force is at its maximum value when the speed is still just zero.
This type of acceleration control, as a part of a stabilization design, has been known for some time in electric drives in which the force acting on the drive train is sensed. In this technique, force is sensed by measuring the elongation of a linear stabilization drive that transmits the torque of the motor through a spindle to a control piston driving the rotational mass.
An adjustment and stabilization unit with a linear control drive and a torque control circuit for stabilizing a weapon system arranged on a vehicle is described in DE 43 17 935 C2. In this unit, the torque signal taken from a spindle or a gear of the driving device is forwarded to a speed controller that acts on the drive motor through the power electronics. In this process, a set of strain gauges is used as a torque sensor. The strain gauges are interconnected in a bridge circuit, and are arranged in the axial and radial directions at the nose of the spindle, at the drive mounting, or at the retaining device of the driving mechanics.
Such linear control drives are primarily employed for the orientation of weapons with a limited adjustment angle in the elevation direction (e.g., with adjustment angles of up to about 40°). In weapon systems with larger elevation adjustment angles of up to about 90° (e.g., for the use on armored vehicles used for air defense), such linear control drives have considerable disadvantages as the gear ratio of the rotational motion of the motor into the slewing motion of the weapon system into the elevation direction effectively increases with the increase of the adjustment angle, making it difficult to compensate for as to its control and drive. Therefore, in weapon systems requiring larger elevation adjustment angles, rotary drives are used which have a constant gear ratio at all adjustment angles.
For measuring torque, devices are known which can be arranged in the drive train of such a linear drive between the rotor of the motor and the rotational mass to be driven. Such an arrangement would require measuring the torque of moving parts, leading to additional complexity for transmitting the measuring signals (e.g., by means of slip rings, trailing cables, radio, etc.) from the rotating part of the drive to the static part of the stabilization unit. Furthermore, such torquemeters must only be loaded by the torques to be measured, so that lateral forces and bending forces are eliminated by means of a complex mechanical integration of the torquemeter.
Torques can also be measured by measuring the reaction torque exerted on the stator of the motor. The stator of the motor does not rotate, and the signal reflecting the measured torque can be transmitted directly to the stabilization control circuit. This avoids the disadvantages that occur when the measuring signal is transmitted from rotating parts. When the reaction moment is measured at the stator of the motor, no torque occurs when the platform moves and the not-yet accelerated rotor is driven by the still-stationary mass. Hence, the acceleration of the of the still-stationary rotational mass can be measured. With respect to high stabilization quality of the stabilization drive, it is this measuring information that is the most important quantity, as the signal of the driven rotational mass has to be processed with the aim of accelerating the rotor in the control circuit as quickly as possible. However, the torque exerted by the rotational mass is not transmitted to the stator of the motor, as the acceleration moments are supported at the still-stationary mass of the rotor.
A suitable sensing element for determining the torques for an adjustment and stabilization unit must not measure any external influences, which may, for example, arise from linear acceleration forces acting on the adjustment drive, as the platform on which the rotational mass is held can undergo accelerations into all directions.
The object of the present invention is to provide an adjustment and stabilization unit with a simple torquemeter device measuring the torques exerted between a rotational mass and a platform, these torques being generated by the drive as well as by the moving platform.